Method of controlling continuous rolling of metal strips

ABSTRACT

In the continuous rolling of a metal strip by means of a plurality of tandem mill stands, the gauge of the strip is varied by varying the rolling speed of a particular mill stand and of suceeding and or preceding mill stands by the same increment when a gauge varying point of the strip reaches the particular mill stand, and then the rolling speeds of the succeeding and/or preceding mill stands are successively varied by the same increment, thereby finally varying the rolling speed of all stands to the speeds required to produce a strip of a given gauge.

United States Patent 1191 Fujii et al.

METHOD OF CONTROLLING CONTINUOUS ROLLING OF METAL STRIPS Inventors: Seiji Fujii; Hiroshi Kuwamoto;

Masayuki Ishida, Fukuyama; Masamoto Kamata, Kawasaki, all of Japan Assignee: Nippon Kokan Kabushiki Kaisha Filed: Feb. 26, 1971 Appl. No.: 119,117

Foreign Application Priority Data Mar. 7, 1970 Japan ..45/l92ll us. c1 "72/16, 72/240 1m. (:1. ..B2lb 37/00 Field ofSearch ..72/8,9, 10,19,11,7,16

References Cited UNITED STATES PATENTS 5/1962 Schwab ..72/ll X STAND 2 STAND 1 GAUG VARYI POINT SENSOR COMPUTER MOTOR SPEED CONTROL Mar. 27, 1973 3,457,747 7/1969 Yeomans ..72 234 3,603,124 9/1971 3,332,263 7/1967 3,531,961 10 1970 3,552,170 1/1971 Pfiefier etal ..72/209 Primary Examiner-Milton S. Mehr Attorney-Flynn & Frishauf [57] ABSTRACT In the continuous rolling of a metal strip by means of a plurality of tandem mill stands, the gauge of the strip is varied by varying the rolling speed of a particular mill stand and of suceeding and or preceding mill stands by the same increment when a gauge varying point of the strip reaches the particular mill stand, and then the rolling speeds of the succeeding and/or preceding mill stands are successively varied by the same increment, thereby finally varying the rolling speed of all stands to the speeds required to produce a strip of a given gauge.

10 Claims, 3 Drawing Figures STANDS SENSOR SPEED MOYOR DETECTORS SPEED SETTERS DIVIDERS SPEED MEMORIES X MULTIPLIERS PATENTEDHARZYISH 3,722,244

SHEET 10F 3 STAND 2 STAND 1 STAND 5 SENSOR NG SPEED DETECTORS POINT SENSOR MOTORS STAND MOTOR S COMPUTER PEED CONTROL STAND ST ND SPEED SETTERS DIVIDERS SPEED MEMORIES 3P 5 SWITCHES MULTIPLI ERS METHOD OF CONTROLLING CONTINUOUS ROLLING OF METAL STRIPS BACKGROUND OF THE INVENTION tandem mill stands wherein when the pass schedule is modified during the rolling operation for varying the gauge of the product. Variations in the tension of the strip are minimized at the transit state during the modification of the pass schedule, thus greatly reducing the possibility of the variations in the plate gauge and the tendency of breaking the plate or sheet.

With the conventional rolling mill control system, in order to perform the so-called stepped rolling, that is to roll different portions of a single coil to have different gauges, the operator is required to manually adjust the gauge settings after either stopping the rolling mill or after slowing down the rolling speed to an extremely low speed.

In modern cold rolling mills, metal strips are continuously rolled by successively welding the leading end of one strip to the trailing end of the preceding strip.

With such a continuous rolling system it is often desirable to change or modify the rolling schedule during the rolling operation.

In order to operate such a continuous rolling mill at the highest efficiency it is not only necessary to increase, as far as possible, the rolling speed but also to modify the rolling schedule without stopping the operation of the rolling mill. For this reason, where the gauge of the starting strip varies or the product gauge is to be varied by varying the reduction rate it is desirable to vary the reduction rate while maintaining the speed of the rolling mill at as high a speed as possible.

Although it is necessary to vary the pass schedule for the purpose of varying the reduction rate, if the rolling schedule were varied quickly when the strip passes through respective mill stands, the tension of the strip will vary greatly and produce a large quantity of offgauge products as well as rupture of the strip.

Also in the stepped rolling, it is essential to vary the reduction rate at a high rolling speed so as to minimize the variation in the tension of the strip in order to improve the rolling efficiency and to reduce off-gauge products.

It is, therefore, an object of this invention to provide a novel method of controlling the continuous rolling operation of a metal strip wherein the variation in the tension of the strip is minimized when the reduction rates are varied.

Another object of this invention is to provide a novel method for controlling the continuous rolling mill operation wherein the gauge or reduction rate may be safely varied during high speed operation.

SUMMARY OF THE INVENTION According to this invention, a method controlling the continuous rolling of a metal strip by means of a plurality of tandem mill stands, comprises the steps of varying the rolling speeds of a particular mill stand and of succeeding and/or preceding mill stands by the same increment when a gauge varying point of the metal strip reaches the particular mill stand, and then successively varying the rolling speeds of the succeeding and/or preceding mill stands by the same increment, thereby finally varying the rolling speeds of all mill stands to the speeds required to produce a strip of a given gauge. All variations are carried out during the continuous rolling process.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 2a and 2b are graphs showing variations in the roll peripheral speeds at respective mill stands.

DESCRIPTION OF THE PREFERRED EMBODIMENT Assume now that rolling speeds of respective mill stands are expressed by V V V V, before varying the pass schedule and by V V V V after varying the pass schedule. The rolling speed of the first mill stand is varied from V to V, when the gauge varying point reaches the first mill stand. Similarly, the rolling speeds of the second, third and the last mill stand are varied from V to V (VJ/V from V to V (VJ/V1) and from V to Vn(V,/V,), respectively. By such adjustments, the rolling speeds of all mill stands are varied by an equal increment, that is V,/V so that the tension of the strip is never varied at any point.

Then, when the gauge varying point reaches the second mill stand, the rolling speed thereof is varied from V (V '/V to V In the same manner, the rolling speed of the third and the last stands are varied from V (VJ/V to V (V /V2) and from V,,(V1/V to V" (Vi/V2); respectively. However, at this time, the rolling speed of the first stand is still maintained at V Although this adjustment varies the tension of the strip between the first and second stands by an amount corresponding to the difference in the reduction rates, it does not vary in any way the tension of the strip between the other stands.

When the gauge varying point arrives at the third mill stand the rolling speeds of the third and last mill stands are varied from V (V '/V to V and from Vn(V '/V to Vn(V /V respectively, but the rolling speeds at the first and second stands are not varied. This adjustment changes the tension of the strip between the second and third stands by an amount proportional to the difference in the reduction rates but does not vary the tension between the other stands.

Generally speaking, when a gauge varying point reaches the No. i mill stand the rolling speeds of the No. i mill stand and of the mill stands on the delivery side are varied as follows.

However, the rolling speeds of the rolling stands on the entry side are not varied. By this adjustment, although thetension of the strip between No. i l stand and No.i stand is varied by an amount proportional to the difference in the reduction rates at these two stands, the tension of the strip between the other stands is not varied.

' schedule. The set data are given automatically from an independent electronic computer 21, a manually operated switch or other suitable device. There are also provided memories 6 to 10 for storing the rolling speeds at respective stands as determined, for example, by speed detectors, before varying the pass schedule. Between respective pairs of speed setters l to and corresponding speed memories 6 to are connected dividers 11 to for providing outputs V '/V V '/V V '/V V /V and V /V respectively. Relay con-. tacts 1P, 2P, 3P, 4P and SP are provided to be closed when the gauge varying point reaches respective mill stands. When the gauge varying point reaches the first stand, relay contact IP is closed to select the output V V1 from divider 11, but outputs from the other dividers are not selected. In the same manner, upon arrival of the gauge varying point at the second, third, fourth and fifth mill stands, respectively, outputs V 'IV V3I/V3, V4,/V4 and V5I/V5 be selected, respectively.

Multipliers 16 to are connected between respectivepairs of dividers 11 to 15 and corresponding memories 6 to 10 for multiplying the outputs from the dividers with the outputs (speeds before schedule variation) from the memories upon receiving command signals from outside. These multipliers are constructed such that they maintain their outputs until the next command signals are supplied thereto when relay contacts IP to 5? are closed.

Said command signals are sent to multipliers 16 to 20 when either one of the contacts I? for the first stand, IP and 2P for the second stand, 1? to 3? for the third stand, I? to 4P for the fourth stand and IP to SP for the fifth stand acts.

The outputs from respective multipliers 16 to 20 are applied to speed control circuits 22 of respective mill 45 stands as the reference signals for speed setting.

Screw down control is achieved in a conventional manner as is illustrated in FIG. 1. Also, forward slip rate is taken into account in predetermining the pass schedule, that is, when predetermining V V V, and V V V,,'.

In the above described system, the rolling speed of a particular mill stand at which the gauge varying point reaches and the rolling speeds of the stands on the delivery side are varied but the rolling speeds of the mill stands on the entry side are not varied. The same object can be attained either by varying at the same rate the rolling speeds of the stands on the entry side while maintaining unchanged the rolling speeds of a particular stand at which the gauge varying point reaches and the speeds of the stands on the delivery side or by varying the rolling speeds of the stands on both entry and delivery sides.

TAB LE 1 Table 1 above shows the speed setting pattern when the rolling speeds are varied on the delivery side whereas table 2 that when the rolling speeds are varied on the entry side.

TABLE 2 Stand at Stand number which gauge varying point arrives 1 Before arrival V Thus, according to this invention, it is possible to vary the gauge of the product while a continuous rolling mill is operating at a high speed, thus greatly improving the operating efficiency. Moreover, it is possible to decrease the possibility of breakage of the strip due to variation in tension.

What is claimed is:

1. In the continuous rolling of a metal strip by means of a plurality of tandem mill stands, a method of controlling the rolling operation comprising the steps of:

detecting a gauge varying point of the metal strip at a given mill stand; varying the rolling speeds of said given mill stand and of succeeding mill stands in the direction of strip movement by the same increment when said gauge varying point of said metal strip reaches said given mill stand;

and then successively varying the rolling speeds of said succeeding mill stands in order by the same increment upon said gauge varying point reaching respective successive mill stands, the rolling speeds of the preceding mill stands not being varied as a function of said gauge varying point reaching said successive mill stands, thereby finally varying the rolling speeds of all mill stands to the speeds required to produce a strip of a given gauge.

2. In the continuous rolling of a metal strip by means of a plurality of tandem mills, a method of controlling the rolling operation comprising the steps of:

detecting a gauge varying point of the metal strip at a given mill stand;

varying the rolling speeds of said given mill stand and of preceding mill stands in the direction opposite to the direction of strip movement by the same increment when said gauge varying point of said metal strip reaches said given mill stand;

and then successively varying the rolling speeds of said preceding mill stands in order by the same increment upon said gauge varying reaching respective successive mill stands, the rolling speeds of the succeeding mill stands in the direction of strip movement not being varied as a function of said gauge varying point reaching each successive mill stand, thereby finally varying the rolling speeds of all stands to the speeds required to produce a strip of a given gauge.

3. The method according to claim 1 comprising detecting said gauge varying point at each mill stand, and varying said speeds responsive to said detection of gauge varying point.

4. The method according to claim 2 comprising detecting said gauge varying point at each mill stand, and

varying said speeds responsive to said detections of gauge varying point.

5. The method according to claim 1 wherein said rolling mill comprises at least three mill stands, and the rolling speed of said three mill stands are varied by the same increment when said gauge varying point of said metal strip reaches the first of said mill stands, and the rolling speeds of the second and third mill stands being varied by the same increment which is different from the first-mentioned increment, when said gauge varying point of said metal strip reaches the second mill stand.

6. The method according to claim 5 wherein the rolling speed of the third mill stand is varied by an increment which is different from the previously mentioned increments when said gauge varying point of said metal strip reaches said third mill stand.

7. The method according to claim 2 wherein said rolling mill comprises at least three mill stands and wherein the rolling speeds of the first mill stand is varied by a given increment when said gauge varying point reaches said first mill stand, and the rolling speeds of said first and second mill stands are varied by the same increment which is different from said given increment when said gauge varying point reaches said second mill stand.

8. The method according to claim 7 wherein the rolling speeds of said three mill stands are varied by the same increment which is different from said previously mentioned increments when said gauge varying point reaches said third mill stand.

9. The method according to claim I wherein the step of varying the rolling speeds comprises determining the rolling speed of the strip at a particular mill stand;

changing the speed at said particular mill stand to a new given value; dividing said new given value'by the determined speed at said particular mill stand; multiplying the ratio obtained by said dividing step by the rolling speed at said successive mill stands; and c0ntrolling the motor speeds at said successive mill stands to correspond to the value obtained by said multiplication.

10. The method according to claim 2 wherein the step of varying the rolling speeds comprises determining the rolling speed of the strip at a particular mill stand; changing the speed at said particular mill stand to a new given value; dividing said new given value by the determined speed at said particular mill stand; multiplying the ratio obtained by said dividing step by the rolling speed at said successive mill stands; and controlling the motor speeds at said preceding mill stands to correspond to the value obtained by said multiplication. 

1. In the continuous rolling of a metal strip by means of a plurality of tandem mill stands, a method of controlling the rolling operation comprising the steps of: detecting a gauge varying point of the metal strip at a given mill stand; varying the rolling speeds of said given mill stand and of succeeding mill stands in the direction of strip movement by the same increment when said gauge varying point of said metal strip reaches said given mill stand; and then successively varying the rolling speeds of said succeeding mill stands in order by the same increment upon said gauge varying point reaching respective successive mill stands, the rolling speeds of the preceding mill stands not being varied as a function of said gauge varying point reaching said successive mill stands, thereby finally varying the rolling speeds of all mill stands to the speeds required to produce a strip of a given gauge.
 2. In the continuous rolling of a metal strip by means of a plurality of tandem mills, a method of controlling the rolling operation comprising the steps of: detecting a gauge varying point of the metal strip at a given mill stand; varying the rolling speeds of said given mill stand and of preceding mill stands in the direction opposite to the direction of strip movement by the same increment when said gauge varying point of said metal strip reaches said given mill stand; and then successively varying the rolling speeds of said preceding mill stands in order by the same increment upon said gauge varying reaching respective successive mill stands, the rolling speeds of the succeeding mill stands in the direction of strip movement not being varied as a function of said gauge varying point reaching each successive mill stand, thereby finally varying the rolling speeds of all stands to the speeds required to produce a strip of a given gauge.
 3. The method according to claim 1 comprising detecting said gauge varying point at each mill stand, and varying said speeds responsive to said detection of gauge varying point.
 4. The method according to claim 2 comprising detecting said gauge varying point at each mill stand, and varying said speeds responsive to said detections of gauge varying point.
 5. The method according to claim 1 wherein said rolling mill comprises at least three mill stands, and the rolling speed of said three mill stands are varied by the same increment when said gauge varying point of said metal strip reaches the first of said mill stands, and the rolling speeds of the second and third mill stands being varied by the same increment which is different from the first-mentioned increment, when said gauge varying point of said metal strip reaches the second mill stand.
 6. The method according to claim 5 wherein the rolling speed of the third mill stand is varied by an increment which is different from the previously mentioned increments when said gauge varying point of said metal strip reaches said third mill stand.
 7. The method according to claim 2 wherein said rolling mill comprises at least three mill stands and wherein the rolling speeds of the first mill stand is varied by a given increment when said gauge varying point reaches said first mill stand, and the rolling speeds of said first and second mill stands are varied by the same increment which is different from said given increment when said gauge varying point reaches said second mill stand.
 8. The method according to claim 7 wherein the rolling speeds of said three mill stands are varied by the same increment which is different from said prevIously mentioned increments when said gauge varying point reaches said third mill stand.
 9. The method according to claim 1 wherein the step of varying the rolling speeds comprises determining the rolling speed of the strip at a particular mill stand; changing the speed at said particular mill stand to a new given value; dividing said new given value by the determined speed at said particular mill stand; multiplying the ratio obtained by said dividing step by the rolling speed at said successive mill stands; and controlling the motor speeds at said successive mill stands to correspond to the value obtained by said multiplication.
 10. The method according to claim 2 wherein the step of varying the rolling speeds comprises determining the rolling speed of the strip at a particular mill stand; changing the speed at said particular mill stand to a new given value; dividing said new given value by the determined speed at said particular mill stand; multiplying the ratio obtained by said dividing step by the rolling speed at said successive mill stands; and controlling the motor speeds at said preceding mill stands to correspond to the value obtained by said multiplication. 